Internet Engineering Task Force (IETF) J. Ryoo
Request for Comments: 8234 T. Cheung
Updates: 7271 ETRI
Category: Standards Track H. van Helvoort
ISSN: 2070-1721 Hai Gaoming BV
I. Busi
G. Wen
Huawei Technologies
August 2017
Internet Engineering Task Force (IETF) J. Ryoo
Request for Comments: 8234 T. Cheung
Updates: 7271 ETRI
Category: Standards Track H. van Helvoort
ISSN: 2070-1721 Hai Gaoming BV
I. Busi
G. Wen
Huawei Technologies
August 2017
Updates to MPLS Transport Profile (MPLS-TP) Linear Protection in Automatic Protection Switching (APS) Mode
在自动保护切换（APS）模式下更新MPLS传输配置文件（MPLS-TP）线性保护
Abstract
摘要
This document contains updates to MPLS Transport Profile (MPLS-TP) linear protection in Automatic Protection Switching (APS) mode defined in RFC 7271. The updates provide rules related to the initialization of the Protection State Coordination (PSC) Control Logic (in which the state machine resides) when operating in APS mode and clarify the operation related to state transition table lookup.
本文档包含RFC 7271中定义的自动保护切换（APS）模式下MPLS传输配置文件（MPLS-TP）线性保护的更新。更新提供了在APS模式下运行时与保护状态协调（PSC）控制逻辑（状态机所在）初始化相关的规则，并澄清了与状态转换表查找相关的操作。
Status of This Memo
关于下段备忘
This is an Internet Standards Track document.
这是一份互联网标准跟踪文件。
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.
本文件是互联网工程任务组（IETF）的产品。它代表了IETF社区的共识。它已经接受了公众审查，并已被互联网工程指导小组（IESG）批准出版。有关互联网标准的更多信息，请参见RFC 7841第2节。
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc8234.
有关本文件当前状态、任何勘误表以及如何提供反馈的信息，请访问http://www.rfc-editor.org/info/rfc8234.
Copyright Notice
版权公告
Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2017 IETF信托基金和确定为文件作者的人员。版权所有。
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)自本文件出版之日起生效。请仔细阅读这些文件，因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本，并提供简化BSD许可证中所述的无担保。
Table of Contents
目录
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
3. Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Updates . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Initialization Behavior . . . . . . . . . . . . . . . . . 5
4.2. State Transition Modification . . . . . . . . . . . . . . 6
4.3. Operation Related to State Transition Table Lookup . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
3. Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Updates . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Initialization Behavior . . . . . . . . . . . . . . . . . 5
4.2. State Transition Modification . . . . . . . . . . . . . . 6
4.3. Operation Related to State Transition Table Lookup . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
MPLS Transport Profile (MPLS-TP) linear protection in Automatic Protection Switching (APS) mode is defined in RFC 7271 [RFC7271]. It defines a set of alternate and additional mechanisms to perform some of the functions of linear protection described in RFC 6378 [RFC6378]. The actions performed at initialization of the Protection State Coordination (PSC) Control Logic are not described in either [RFC7271] or [RFC6378]. Although it is a common perception that the state machine starts at the Normal state, this is not explicitly specified in any of the documents and various questions have been raised by implementers and in discussions on the MPLS working group mailing list concerning the detailed actions that the PSC Control Logic should take.
RFC 7271[RFC7271]中定义了自动保护切换（APS）模式下的MPLS传输配置文件（MPLS-TP）线性保护。它定义了一组替代和附加机制，以执行RFC 6378[RFC6378]中描述的线性保护功能。[RFC7271]或[RFC6378]中均未描述初始化保护状态协调（PSC）控制逻辑时执行的操作。尽管通常认为状态机在正常状态下启动，但在任何文件中都没有明确规定，实施者和MPLS工作组邮件列表讨论中提出了各种问题，涉及PSC控制逻辑应采取的详细行动。
The state machine described in [RFC7271] operates under the assumption that both end nodes of a linear protection domain start in the Normal state. In the case that one node reboots while the other node is still in operation, various scenarios may arise resulting in problematic situations. This document resolves all the problematic cases and minimizes traffic disruptions related to initialization, including both cold and warm reboots that require re-initialization of the PSC Control Logic.
[RFC7271]中描述的状态机在假设线性保护域的两个端节点都以正常状态启动的情况下运行。在一个节点重新启动而另一个节点仍在运行的情况下，可能会出现各种情况，导致出现问题。本文档解决了所有有问题的情况，并最大限度地减少了与初始化相关的通信中断，包括需要重新初始化PSC控制逻辑的冷重启和热重启。
This document contains updates to the MPLS-TP linear protection in APS mode defined in [RFC7271]. The updates provide rules related to initialization of the PSC Control Logic (in which the state machine resides) when operating in APS mode. The updates also include modifications to the state transition table defined in Section 11.2 of [RFC7271]. The changes in the state transition table have been examined to make sure that no new problems are introduced.
本文件包含[RFC7271]中定义的APS模式下MPLS-TP线性保护的更新。更新提供了在APS模式下运行时与PSC控制逻辑（状态机所在）初始化相关的规则。更新还包括对[RFC7271]第11.2节中定义的状态转换表的修改。已检查状态转换表中的更改，以确保不会引入新问题。
This document does not introduce backward compatibility issues with implementations of [RFC7271]. In case a node implementing this document restarts, the new state changes will not cause problems at the remote node implementing [RFC7271], and the two ends will converge to the same local and remote states. In case a node implementing [RFC7271] restarts, the two ends behave as they do today.
本文档不介绍[RFC7271]实现的向后兼容性问题。如果实现本文档的节点重新启动，新的状态更改将不会在实现[RFC7271]的远程节点上引起问题，并且两端将聚合到相同的本地和远程状态。如果实现[RFC7271]的节点重新启动，两端的行为与今天一样。
This document also provides some clarifications on the operation related to state transition table lookup.
本文档还对与状态转换表查找相关的操作进行了一些说明。
The reader of this document is assumed to be familiar with [RFC7271].
假定本文件的读者熟悉[RFC7271]。
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
本文件中的关键词“必须”、“不得”、“必需”、“应”、“不应”、“建议”、“不建议”、“可”和“可选”在所有大写字母出现时（如图所示）应按照BCP 14[RFC2119][RFC8174]所述进行解释。
This document uses the following abbreviations:
本文件使用以下缩写：
APS Automatic Protection Switching DNR Do-not-Revert E::R Exercise state due to remote EXER message EXER Exercise MS-P Manual Switch to Protection path MS-W Manual Switch to Working path MPLS-TP MPLS Transport Profile NR No Request PF:DW:R Protecting Failure state due to remote SD-W message PF:W:L Protecting Failure state due to local SF-W PF:W:R Protecting Failure state due to remote SF-W message PSC Protection State Coordination RR Reverse Request SA:MP:R Switching Administrative state due to remote MS-P message SA:MW:R Switching Administrative state due to remote MS-W message SD Signal Degrade SD-W Signal Degrade on Working path SF Signal Fail SF-P Signal Fail on Protection path SF-W Signal Fail on Working path UA:P:L Unavailable state due to local SF-P WTR Wait-to-Restore
APS自动保护切换DNR不恢复E:：R由于远程EXER消息EXER EXERSE MS-P手动切换到保护路径MS-W手动切换到工作路径MPLS-TP MPLS传输配置文件NR无请求PF:DW:R由于远程SD-W消息PF:W:L保护故障状态由于本地SF-W PF:W:R由于远程SF-W消息导致的保护故障状态PSC保护状态协调RR反向请求SA:MP:R由于远程MS-P消息导致的切换管理状态SA:MW:R由于远程MS-W消息导致的切换管理状态SD信号降级SD-W信号在工作路径上降级SF信号失败SF-P信号在保护路径上失败SF-W由于本地SF-P WTR等待恢复，工作路径UA:P:L不可用状态上的信号失败
This section specifies the actions that will be performed at the initialization of the PSC Control Logic and the modifications of the state transition table defined in Section 11.2 of [RFC7271]. Some clarifications on the operation related to state transition table lookup are also provided.
本节规定了在初始化PSC控制逻辑和修改[RFC7271]第11.2节中定义的状态转换表时将执行的操作。还提供了与状态转换表查找相关的操作的一些说明。
This section defines initialization behavior that is not described in [RFC7271].
本节定义了[RFC7271]中未描述的初始化行为。
When the PSC Control Logic is initialized, the following actions MUST be performed:
初始化PSC控制逻辑时，必须执行以下操作：
o Stop the WTR timer if it is running.
o 如果WTR计时器正在运行，请停止该计时器。
o Clear any operator command in the Local Request Logic.
o 清除本地请求逻辑中的任何操作员命令。
o If an SF-W or SF-P exists as the highest local request, the node being initialized starts at the PF:W:L or UA:P:L state, respectively.
o 如果SF-W或SF-P作为最高本地请求存在，则被初始化的节点分别从PF:W:L或UA:P:L状态开始。
o If the node being initialized has no local request:
o 如果正在初始化的节点没有本地请求：
* If the node being initialized does not remember the active path or if the node being initialized remembers the working path as the active path, the node starts at the Normal state.
* 如果正在初始化的节点不记得活动路径，或者如果正在初始化的节点记得工作路径是活动路径，则节点将以正常状态启动。
* Else (the node being initialized remembers the protection path as the active path), the node starts at the WTR state sending NR(0,1) or at the DNR state sending DNR(0,1) depending on the configuration that allows or prevents automatic reversion to the Normal state.
* 否则（被初始化的节点将保护路径记为活动路径），节点从WTR状态发送NR（0,1）或DNR状态发送DNR（0,1）开始，具体取决于允许或防止自动恢复到正常状态的配置。
o In case any local SD exists, the local SD MUST be considered as an input to the Local Request Logic only after the local node has received the first protocol message from the remote node and completed the processing (i.e., updated the PSC Control Logic and decided which action, if any, is to be sent to the PSC Message Generator).
o 如果存在任何本地SD，则只有在本地节点从远程节点接收到第一条协议消息并完成处理（即，更新PSC控制逻辑并决定将哪个动作（如果有的话）发送到PSC消息生成器）之后，才必须将本地SD视为本地请求逻辑的输入。
o If the local node receives an EXER message as the first protocol message after initialization and the remote EXER becomes the top-priority global request, the local node MUST set the position of the bridge and selector according to the Path value in the EXER message and transit to the E::R state.
o 如果本地节点在初始化后接收到作为第一个协议消息的EXER消息，并且远程EXER成为最高优先级的全局请求，则本地节点必须根据EXER消息中的路径值设置桥接器和选择器的位置，并过渡到E:：R状态。
In the case of no local request, remembering the active path minimizes traffic switchovers when the remote node is still in operation. This approach does not cause a problem even if the remembered active path is no longer valid due to any local input that occurred at the remote node while the initializing node was out of operation.
在没有本地请求的情况下，当远程节点仍在运行时，记住活动路径可以最大限度地减少流量切换。即使由于初始化节点停止运行时远程节点上发生的任何本地输入，所记住的活动路径不再有效，这种方法也不会导致问题。
Note that in some restart scenarios (e.g., cold rebooting), no valid SF/SD indications may be present at the input of the Local Request Logic. In this case, the PSC Control Logic restarts as if no local requests are present. If a valid SF/SD indication is detected later, the PSC Control Logic is notified and state change is triggered.
注意，在某些重启场景中（例如，冷重启），本地请求逻辑的输入处可能不存在有效的SF/SD指示。在这种情况下，PSC控制逻辑重新启动，就好像没有本地请求一样。如果随后检测到有效的SF/SD指示，则通知PSC控制逻辑并触发状态更改。
In addition to the initialization behavior described in Section 4.1, four cells of the remote state transition table need to be changed to make two end nodes converge after initialization. State transition by remote message as defined in Section 11.2 of [RFC7271] is modified as follows (only modified cells are shown):
除了第4.1节中描述的初始化行为外，还需要更改远程状态转换表的四个单元格，以使两个终端节点在初始化后聚合。[RFC7271]第11.2节中定义的远程消息状态转换修改如下（仅显示修改后的单元格）：
| MS-W | MS-P | WTR | EXER | RR | DNR | NR
--------+---------+---------+-----+------+----+------+----
N | | | (13)| | | DNR |
PF:W:R | | | | | | DNR |
PF:DW:R | | | | | | DNR |
| MS-W | MS-P | WTR | EXER | RR | DNR | NR
--------+---------+---------+-----+------+----+------+----
N | | | (13)| | | DNR |
PF:W:R | | | | | | DNR |
PF:DW:R | | | | | | DNR |
The changes in two rows of remote protecting failure states lead to the replacement of note (10) with DNR; therefore, note (10) is no longer needed. The resultant three rows read:
两行远程保护故障状态的变化导致注释（10）替换为DNR；因此，不再需要注释（10）。结果三行为：
| MS-W | MS-P | WTR | EXER | RR | DNR | NR
--------+---------+---------+-----+------+----+------+----
N | SA:MW:R | SA:MP:R | (13)| E::R | i | DNR | i
PF:W:R | SA:MW:R | SA:MP:R | (9) | E::R | i | DNR | (11)
PF:DW:R | SA:MW:R | SA:MP:R | (9) | E::R | i | DNR | (11)
| MS-W | MS-P | WTR | EXER | RR | DNR | NR
--------+---------+---------+-----+------+----+------+----
N | SA:MW:R | SA:MP:R | (13)| E::R | i | DNR | i
PF:W:R | SA:MW:R | SA:MP:R | (9) | E::R | i | DNR | (11)
PF:DW:R | SA:MW:R | SA:MP:R | (9) | E::R | i | DNR | (11)
In the tables above, the letters 'i' and 'N' stand for "ignore" and "Normal state", respectively. Other abbreviations can be found in Section 3.
在上表中，字母“i”和“N”分别代表“忽略”和“正常状态”。其他缩略语见第3节。
In addition to the rules related to the state transition table lookup listed in Section 11 of [RFC7271], the following rule is also applied to the operation related to the state transition table lookup:
除了[RFC7271]第11节中列出的与状态转换表查找相关的规则外，以下规则也适用于与状态转换表查找相关的操作：
o When the local SF-P is cleared and the priorities of the local and remote requests are re-evaluated, the last received remote message may no longer be valid due to the previous failure of the protection path. Therefore, the last received message MUST be treated as if it were NR and only the local request shall be evaluated.
o 当清除本地SF-P并重新评估本地和远程请求的优先级时，由于之前的保护路径故障，最后收到的远程消息可能不再有效。因此，必须将最后收到的消息视为NR，并且仅对本地请求进行评估。
The last paragraph in Section 11 of [RFC7271] is modified as follows:
[RFC7271]第11节最后一段修改如下：
---------
Old text:
---------
In the state transition tables below, the letter 'i' stands for
"ignore" and is an indication to remain in the current state and
continue transmitting the current PSC message.
---------
Old text:
---------
In the state transition tables below, the letter 'i' stands for
"ignore" and is an indication to remain in the current state and
continue transmitting the current PSC message.
---------
New text:
---------
In the state transition tables below, the letter 'i' is the
"ignore" flag; if it is set, it means that the top-priority
global request is ignored.
---------
New text:
---------
In the state transition tables below, the letter 'i' is the
"ignore" flag; if it is set, it means that the top-priority
global request is ignored.
If re-evaluation is triggered, the ignore flag is checked. If it is set, the state machine will transit to the supposed state, which can be Normal or DNR as indicated in the footnotes to the state transition table in Section 11.1 of [RFC7271]. If the ignore flag is not set, the state machine will transit to the state indicated in the cell of the state transition table.
如果触发重新评估，则选中忽略标志。如果设置，状态机将转换到假定状态，该状态可以是正常或DNR，如[RFC7271]第11.1节状态转换表脚注所示。如果未设置忽略标志，状态机将转换到状态转换表单元格中指示的状态。
If re-evaluation is not triggered, the ignore flag is checked. If it is set, the state machine will remain in the current state, and the current PSC message continues to be transmitted. If the ignore flag is not set, the state machine will transit to the state indicated in the cell of the state transition table.
如果未触发重新评估，则选中忽略标志。如果设置，状态机将保持当前状态，并且当前PSC消息将继续传输。如果未设置忽略标志，状态机将转换到状态转换表单元格中指示的状态。
No specific security issue is raised in addition to those ones already documented in [RFC7271]. Note that tightening the description of the initializing behavior may help to protect networks from restart attacks.
除[RFC7271]中已记录的安全问题外，未提出任何具体的安全问题。请注意，加强对初始化行为的描述可能有助于保护网络免受重启攻击。
This document does not require any IANA actions.
本文件不要求IANA采取任何行动。
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>.
[RFC2119]Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，DOI 10.17487/RFC2119，1997年3月<https://www.rfc-editor.org/info/rfc2119>.
[RFC7271] Ryoo, J., Ed., Gray, E., Ed., van Helvoort, H., D'Alessandro, A., Cheung, T., and E. Osborne, "MPLS Transport Profile (MPLS-TP) Linear Protection to Match the Operational Expectations of Synchronous Digital Hierarchy, Optical Transport Network, and Ethernet Transport Network Operators", RFC 7271, DOI 10.17487/RFC7271, June 2014, <https://www.rfc-editor.org/info/rfc7271>.
[RFC7271]Ryoo，J.，Ed.，Gray，E.，Ed.，van Helvoort，H.，D'Alessandro，A.，Cheung，T.，和E.Osborne，“MPLS传输配置文件（MPLS-TP）线性保护，以满足同步数字体系、光传输网络和以太网传输网络运营商的运营期望”，RFC 7271，DOI 10.17487/RFC72712014年6月， <https://www.rfc-editor.org/info/rfc7271>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8174]Leiba，B.，“RFC 2119关键词中大写与小写的歧义”，BCP 14，RFC 8174，DOI 10.17487/RFC8174，2017年5月<https://www.rfc-editor.org/info/rfc8174>.
[RFC6378] Weingarten, Y., Ed., Bryant, S., Osborne, E., Sprecher, N., and A. Fulignoli, Ed., "MPLS Transport Profile (MPLS-TP) Linear Protection", RFC 6378, DOI 10.17487/RFC6378, October 2011, <https://www.rfc-editor.org/info/rfc6378>.
[RFC6378]Y.Weingarten，Ed.，Bryant，S.，Osborne，E.，Sprecher，N.，和A.Fulignoli，Ed.，“MPLS传输模式（MPLS-TP）线性保护”，RFC 6378，DOI 10.17487/RFC6378，2011年10月<https://www.rfc-editor.org/info/rfc6378>.
Acknowledgements
致谢
The authors would like to thank Joaquim Serra for raising the issue related to initialization of the PSC Control Logic at the very beginning. The authors would also like to thank Adrian Farrel and Loa Andersson for their valuable comments and suggestions on this document.
作者要感谢Joaquim Serra在一开始就提出了与PSC控制逻辑初始化相关的问题。作者还要感谢Adrian Farrel和Loa Andersson对本文件提出的宝贵意见和建议。
Authors' Addresses
作者地址
Jeong-dong Ryoo ETRI
郑东良
Email: ryoo@etri.re.kr
Email: ryoo@etri.re.kr
Taesik Cheung ETRI
张大世
Email: cts@etri.re.kr
Email: cts@etri.re.kr
Huub van Helvoort Hai Gaoming BV
Huub van Helvoort Hai Gaoming BV
Email: huubatwork@gmail.com
Email: huubatwork@gmail.com
Italo Busi Huawei Technologies
Italo Busi华为技术有限公司
Email: Italo.Busi@huawei.com
Email: Italo.Busi@huawei.com
Guangjuan Wen Huawei Technologies
华为技术有限公司
Email: wenguangjuan@huawei.com
Email: wenguangjuan@huawei.com